6-Alkyl and aryl)-3-mercapto-4-amino-1,2,4-triazinones are known and, with their various derivatives, are an important class of herbicides (U.S. Pat. No. 3,966,715; Chem. Ber. 97, 2173 (1964). Such triazinones are customarily prepared by the reaction of thiocarbohydrazide with .alpha.-ketoacids in neutral solutions at 90.degree.-100.degree. C. Neither 6-carboxy- nor any 6-(.omega.-carboxyalkyl), i.e. 6-HOOC(CH.sub.2).sub.n -, triazinone has been prepared by this process nor have any such compounds been described in the literature. It is noted that 6-carbalkoxyalkyl (i.e., ROOCCH.sub.2 --) esters have been described as has also the uniquely sterically hindered and thus unreactive 6-(o-carboxyphenyl) derivative (U.S. Pat. No. 4,252,944). It is also known that some of the .alpha.-ketodicarboxylic acid reactants required for the preparation of the products of this invention are easily decarboxylated and base sensitive and would not survive the previously described techniques and conditions used for the preparation of triazinones.